arXiv subjects

Jonathan Carroll-Nellenback

Publications and source records attributed to Jonathan Carroll-Nellenback.

At least 19 recordsLinked to original sources

arXiv2025

Validation of FLASH for magnetically driven inertial confinement fusion target design

FLASH is a widely available radiation magnetohydrodynamics code used for astrophysics, laboratory plasma science, high energy density physics, and inertial confinement fusion. Increasing interest in magnetically driven inertial confinement fusion (ICF), including Pacific Fusion's development of a 60 MA Demonstration System designed to achieve facility gain, motivates the improvement and validation of FLASH for modeling magnetically driven ICF concepts, such as MagLIF, at ignition scale. Here we present a collection of six validation benchmarks from experiments at the Z Pulsed Power Facility and theoretical and simulation studies of scaling MagLIF to high currents. The benchmarks range in complexity from focused experiments of linear hydrodynamic instabilities to fully integrated MagLIF fusion experiments. With the latest addition of physics capabilities, FLASH now obtains good agreement with the experimental data, theoretical results, and leading ICF target design simulation code results across all six benchmarks. These results establish confidence in FLASH as a useful tool for designing magnetically driven ICF targets on facilities like Z and Pacific Fusion's upcoming Demonstration System.

physics.plasm-ph↗

arXiv2025

Early solar wind and dynamo magnetic field topology predictions for (16) Psyche and other asteroids

Asteroid (16) Psyche is a metal-rich body that might record an ancient coherent magnetization if some relict crust or mantle is preserved. Herein, we use magnetohydrodynamic simulations to predict (16) Psyche's field topology for several distinct pathways, (i) an early solar wind-induced magnetization imparted after a larger body was impacted, forming the present-day asteroid, (ii) a core dynamo magnetization imparted in an asteroid that is either presently largely intact or was a rubble pile, and (iii) magnetization in the turbulent solar nebula disk. For pathway (i) we find the field to be predominantly dipolar and spin axis-aligned. For pathway (ii) we find the field to be either dipolar and spin axis-misaligned, or highly multipolar. We also find that (iii) a field produced earlier before the solar nebula cleared, would be highly multipolar. In cases (i) and (ii) we also place constraints on the field strength. Simple detection of a magnetic field without constraining its topology and temporal variability would be insufficient to confirm a remanent source, due to the influence of the present-day solar wind, electromagnetic induction, and (16) Psyche's high obliquity. For sufficiently strong fields however, the field topology and orientation may reveal key observable consequences of the nature and history of (16) Psyche. Our framework is also broadly applicable to the study of magnetic fields from other asteroids.

astro-ph.EP↗

arXiv2024

Terrestrial atmospheric ion implantation occurred in the nearside lunar regolith during the history of Earth's dynamo

Light volatile elements in lunar regolith are thought to be a mixture of the solar wind and Earth's atmosphere, the latter sourced in the absence of geomagnetic field. However, the extent to which both the current and primitive geodynamo influence the transport of terrestrial ions still remains unclear, and this uncertainty is further complicated by the enigmatic composition and poorly constrained location of the Eoarchean exosphere. Here we use 3-D MHD numerical simulations with present-day magnetized and Archean unmagnetized atmospheres to investigate how Earth's intrinsic magnetic field affects this transfer, aiming to constrain how and when the lunar isotopic signature provides a record of Earth's paleoatmosphere. We find that atmospheric transfer is efficient only when the Moon is within Earth's magnetotail. The non-solar contribution to the lunar soil is best explained by implantation during the long history of the geodynamo, rather than any short, putatively unmagnetized epoch of early Earth. This further suggests the history of the terrestrial atmosphere, spanning billions of years, could be preserved in buried lunar soils. Our results indicate that the elemental abundances of Apollo samples are very sensitive to Earth's exobase altitude, which, at the time of ion implantation, was never smaller than 190 km.

astro-ph.EP↗

arXiv2024

How negative feedback and the ambient environment limit the influence of recombination in common envelope evolution

We perform 3D hydrodynamical simulations to study recombination and ionization during the common envelope (CE) phase of binary evolution, and develop techniques to track the ionic transitions in time and space. We simulate the interaction of a $2\,M_\odot$ red giant branch primary and a $1\,M_\odot$ companion modeled as a particle. We compare a run employing a tabulated equation of state (EOS) that accounts for ionization and recombination, with a run employing an ideal gas EOS. During the first half of the simulations, $\sim15$ per cent more mass is unbound in the tabulated EOS run due to the release of recombination energy, but by simulation end the difference has become negligible. We explain this as being a consequence of (i) the tabulated EOS run experiences a shallower inspiral and hence smaller orbital energy release at late times because recombination energy release expands the envelope and reduces drag, and (ii) collision and mixing between expanding envelope gas, ejecta and circumstellar ambient gas assists in unbinding the envelope, but does so less efficiently in the tabulated EOS run where some of the energy transferred to bound envelope gas is used for ionization. The rate of mass unbinding is approximately constant in the last half of the simulations and the orbital separation steadily decreases at late times. A simple linear extrapolation predicts a CE phase duration of $\sim2\,\mathrm{yr}$, after which the envelope would be unbound.

astro-ph.SR↗

arXiv2023

Semantic Information in a model of Resource Gathering Agents

We explore the application of a new theory of Semantic Information to the well-motivated problem of a resource foraging agent. Semantic information is defined as the subset of correlations, measured via the transfer entropy, between agent $A$ and environment $E$ that is necessary for the agent to maintain its viability $V$. Viability, in turn, is endogenously defined as opposed to the use of exogenous quantities like utility functions. In our model, the forager's movements are determined by its ability to measure, via a sensor, the presence of an individual unit of resource, while the viability function is its expected lifetime. Through counterfactual interventions -- scrambling the correlations between agent and environment via noising the sensor -- we demonstrate the presence of a critical value of the noise parameter, $η_c$, above which the forager's expected lifetime is dramatically reduced. On the other hand, for $η< η_c$ there is little-to-no effect on its ability to survive. We refer to this boundary as the semantic threshold, quantifying the subset of agent-environment correlations that the agent actually needs to maintain its desired state of staying alive. Each bit of information affects the agent's ability to persist both above and below the semantic threshold. Modeling the viability curve and its semantic threshold via forager/environment parameters, we show how the correlations are instantiated. Our work provides a useful model for studies of established agents in terms of semantic information. It also shows that such semantic thresholds may prove useful for understanding the role information plays in allowing systems to become autonomous agents.

cond-mat.stat-mech↗

arXiv2022

Opportunities for Technosignature Science in the Planetary Science and Astrobiology Decadal Survey

Solar system exploration provides numerous possibilities for advancing technosignature science. The search for life in the solar system includes missions designed to search for evidence of biosignatures on other planetary bodies, but many missions could also attempt to search for and constrain the presence of technology within the solar system. Technosignatures and biosignatures represent complementary approaches toward searching for evidence of life in our solar neighborhood, and beyond. This report summarizes the potential technosignature opportunities within ongoing solar system exploration and the recommendations of the "Origins, Worlds, and Life" Planetary Science and Astrobiology Decadal Survey. We discuss opportunities for constraining the prevalence of technosignatures within the solar system using current or future missions at negligible additional cost, and we present a preliminary assessment of gaps that may exist in the search for technosignatures within the solar system.

astro-ph.IM↗

arXiv2022

Jets from main sequence and white dwarf companions during common envelope evolution

It has long been speculated that jet feedback from accretion onto the companion during a common envelope (CE) event could affect the orbital evolution and envelope unbinding process, but this conjecture has heretofore remained largely untested. We present global 3D hydrodynamical simulations of CE evolution (CEE) that include a jet subgrid model and compare them with an otherwise identical model without a jet. Our binary consists of a $2M_\odot$ red giant branch primary and a $1M_\odot$ or $0.5M_\odot$ main sequence or white dwarf secondary companion modeled as a point particle. We run the simulations for 10 orbits (40 days). Our jet model adds mass at a constant rate $\dot{M}_\mathrm{j}$ of order the Eddington rate, with maximum velocity $v_\mathrm{j}$ of order the escape speed, to two spherical sectors with the jet axis perpendicular to the orbital plane, and supplies kinetic energy at the rate $\sim\dot{M}_\mathrm{j} v_\mathrm{j}^2/40$. We explore the influence of the jet on orbital evolution, envelope morphology and envelope unbinding, and assess the dependence of the results on jet mass-loss rate, launch speed, companion mass, opening angle, and whether or not subgrid accretion is turned on. In line with our theoretical estimates, we find that in all cases the jet becomes choked around the time of first periastron passage. We also find that jets lead to increases in unbound mass of up to $\sim10\%$, as compared to simulations which do not include a jet.

astro-ph.SR↗

arXiv2022

Effects of Charge Exchange on the Evaporative Wind of HD 209458b

The role of charge exchange in shaping exoplanet photoevaporation remains a topic of contention. Exchange of electrons between stellar wind protons from the exoplanet's host star and neutral hydrogen from the planet's wind has been proposed as a mechanism to create "energetic neutral atoms" (ENAs), which could explain the high absorption line velocities observed in systems where mass loss is occurring. In this paper we present results from 3D hydrodynamic simulations of the mass loss of a planet similar to HD 209458b. We self-consistently launch a planetary wind by calculating the ionization and heating resulting from incident high-energy radiation, inject a stellar wind into the simulation, and allow electron exchange between the stellar and planetary winds. We predict the potential production of ENAs by the wind-wind interaction analytically, then present the results of our simulations, which confirm the analytic limits. Within the limits of our hydrodynamic simulation, we find that charge exchange with the stellar wind properties examined here is unable to explain the absorption observed at high Doppler velocities.

astro-ph.EP↗

arXiv2022

Consensus between Epistemic Agents is Difficult

We introduce an epistemic information measure between two data streams, that we term $influence$. Closely related to transfer entropy, the measure must be estimated by epistemic agents with finite memory resources via sampling accessible data streams. We show that even under ideal conditions, epistemic agents using slightly different sampling strategies might not achieve consensus in their conclusions about which data stream is influencing which. As an illustration, we examine a real world data stream where different sampling strategies result in contradictory conclusions, explaining why some politically charged topics might exist due to purely epistemic reasons irrespective of the actual ontology of the world.

physics.soc-ph↗

arXiv2021

Asteroid Magnetization from the Early Solar Wind

Magnetic fields provide an important probe of the thermal, material, and structural history of planetary and sub-planetary bodies. Core dynamos are a potential source of magnetic fields for differentiated bodies, but evidence of magnetization in undifferentiated bodies requires a different mechanism. Here we study the amplified field provided by the stellar wind to an initially unmagnetized body using analytic theory and numerical simulations, employing the resistive MHD AstroBEAR adaptive mesh refinement (AMR) multiphysics code. We obtain a broadly applicable scaling relation for the peak magnetization achieved once a wind advects, piles-up, and drapes a body with magnetic field, reaching a quasi-steady state. We find that the dayside magnetic field for a sufficiently conductive body saturates when it balances the sum of incoming solar wind ram, magnetic, and thermal pressures. Stronger amplification results from pileup by denser and faster winds. Careful quantification of numerical diffusivity is required for accurately interpreting the peak magnetic field strength from simulations, and corroborating with theory. As specifically applied to the Solar System, we find that early solar wind-induced field amplification is a viable source of magnetization for observed paleointensities in meteorites from some undifferentiated bodies. This mechanism may also be applicable to other Solar System bodies, including metal-rich bodies to be visited in future space missions such as the asteroid (16) Psyche.

astro-ph.EP↗

arXiv2021

The Formation of Discs in the Interior of AGB Stars from the Tidal Disruption of Planets and Brown Dwarfs

A significant fraction of isolated white dwarfs host magnetic fields in excess of a MegaGauss. Observations suggest that these fields originate in interacting binary systems where the companion is destroyed thus leaving a singular, highly-magnetized white dwarf. In post-main-sequence evolution, radial expansion of the parent star may cause orbiting companions to become engulfed. During the common envelope phase, as the orbital separation rapidly decreases, low-mass companions will tidally disrupt as they approach the giant's core. We hydrodynamically simulate the tidal disruption of planets and brown dwarfs, and the subsequent accretion disc formation, in the interior of an asymptotic giant branch star. These dynamically formed discs are commensurate with previous estimates, suggesting strong magnetic fields may originate from these tidal disruption events.

astro-ph.SR↗

arXiv2021

Triggering A Climate Change Dominated "Anthropocene": Is It Common Among Exocivilizations?

We seek to model the coupled evolution of a planet and a civilization through the era when energy harvesting by the civilization drives the planet into new and adverse climate states. In this way we ask if triggering "anthropocenes" of the kind humanity is experiencing now might be a generic feature of planet-civilization evolution. In this study we focus on the effects of energy harvesting via combustion and vary the planet's initial atmospheric chemistry and orbital radius. In our model, energy harvesting increases the civilization's population growth rate while also, eventually, leading to a degradation of the planetary climate state (relative to the civilization's habitability.) We also assume the existence of a Complex Life Habitable Zone in which very high levels of $CO_2$ are detrimental to multi-cellular animal life such as those creating technological civilizations. Our models show that the civilization's growth is truncated by planetary feedback (a "climate dominated anthropocene") for a significant region of the initial parameter space.

astro-ph.EP↗

arXiv2020

Bipolar Planetary Nebulae from Outflow Collimation by Common Envelope Evolution

The morphology of bipolar planetary nebulae (PNe) can be attributed to interactions between a fast wind from the central engine and dense toroidal shaped ejecta left over from common envelope (CE) evolution. Here we use the 3-D hydrodynamic AMR code AstroBEAR to study the possibility that bipolar PN outflows can emerge collimated even from an uncollimated spherical wind in the aftermath of a CE event. The output of a single CE simulation via the SPH code PHANTOM serves as the initial conditions. Four cases of winds, all with high enough momenta to account for observed high momenta preplanetary nebula outflows, are injected spherically from the region of the CE binary remnant into the ejecta. We compare cases with two different momenta and cases with no radiative cooling versus application of optically thin emission via a cooling curve to the outflow. Our simulations show that in all cases highly collimated bipolar outflows result from deflection of the spherical wind via the interaction with the CE ejecta. Significant asymmetries between the top and bottom lobes are seen in all cases. The asymmetry is strongest for the lower momentum case with radiative cooling. While real post CE winds may be aspherical, our models show that collimation via "inertial confinement" will be strong enough to create jet-like outflows even beginning with maximally uncollimated drivers. Our simulations reveal detailed shock structures in the shock focused inertial confinement (SFIC) model and develop a lens-shaped inner shock that is a new feature of SFIC driven bipolar lobes.

astro-ph.SR↗

arXiv2020

Common Envelope Evolution on the Asymptotic Giant Branch: Unbinding within a Decade?

Common envelope (CE) evolution is a critical but still poorly understood progenitor phase of many high-energy astrophysical phenomena. Although 3D global hydrodynamic CE simulations have become more common in recent years, those involving an asymptotic giant branch (AGB) primary are scarce, due to the high computational cost from the larger dynamical range compared to red giant branch (RGB) primaries. But CE evolution with AGB progenitors is desirable to simulate because such events are the likely progenitors of most bi-polar planetary nebulae (PNe), and prominent observational testing grounds for CE physics. Here we present a high resolution global simulation of CE evolution involving an AGB primary and $1\,\mathrm{M}_\odot$ secondary, evolved for $20$ orbital revolutions. During the last $16$ of these orbits, the envelope unbinds at an almost constant rate of about $0.1$-$0.2\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$. If this rate were maintained, the envelope would be unbound in less than $10\,\mathrm{yr}$. The dominant source of this unbinding is consistent with inspiral; we assess the influence of the ambient medium to be subdominant. We compare this run with a previous run that used an RGB phase primary evolved from the same $2\,\mathrm{M}_\odot$ main sequence star to assess the influence of the evolutionary state of the primary. When scaled appropriately, the two runs are quite similar, but with some important differences.

astro-ph.SR↗

arXiv2020

A 3D radiation-hydrodynamic AGB binary model

The origin of chemically peculiar stars and non-zero eccentricity in evolved close binaries have been long-standing problems in binary stellar evolution. Answers to these questions may trace back to an intense mass transfer during AGB binary phase. In this work, we use AstroBEAR to solve the 3D radiation-hydrodynamic equations and calculate the mass transfer rate in asymptotic-giant-branch (AGB) binaries that undergo the wind-Roche-lobe-overflow or Bondi-Hoyle-Lyttleton (BHL) accretion. MESA produces the density and temperature of the boundary condition of the AGB star. To improve the resolution of the dynamics of a circumbinary disk, we implement an azimuthal angle-dependent 3D radiation transfer. We consider optically thin cooling and obtain the number density of the coolants by solving Saha equations. One of the goals of this work is to illustrate the transition from the wind-Roche-lobe-overflow to BHL accretion. Both circumbinary disks and spiral structure outflows can appear in the simulations. Circumbinary disks may form when the optical thickness in the equatorial region increases. The increase of the optical thickness is due to the deflected wind. The resulting mass transfer efficiency in our models is up to a factor of 8 times higher than what the standard BHL accretion scenario predicts, and the outflow gains up to 91% of its initial angular momentum when it reaches 1.3 binary separations. Consequently, some AGB binaries may undergo orbit shrinkage, and some will expand. The high mass transfer efficiency is closely related to the presence of the circumbinary disks.

astro-ph.SR↗

arXiv2020

The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion and Steady States

We model the settlement of the galaxy by space-faring civilizations in order to address issues related to the Fermi Paradox. We explore the problem in a way that avoids assumptions about the intent and motivation of any exo-civilization seeking to settle other planetary systems. We first consider the speed of an advancing settlement via probes of finite velocity and range to determine if the galaxy can become inhabited with space-faring civilizations on timescales shorter than its age. We also include the effect of stellar motions on the long term behavior of the settlement front which adds a diffusive component to its advance. The results of these models demonstrate that the Milky Way can be readily 'filled-in' with settled stellar systems under conservative assumptions about interstellar spacecraft velocities and launch rates. We then consider the question of the galactic steady-state achieved in terms of the fraction of settled planets. We do this by considering the effect of finite settlement civilization lifetimes on the steady states. We find a range of parameters for which the galaxy supports a population of interstellar space-faring civilizations even though some settleable systems are uninhabited. Both results point to ways in which Earth might remain unvisited in the midst of an inhabited galaxy. Finally we consider how our results can be combined with the finite horizon for evidence of previous settlements in Earth's geologic record. Our steady-state model can constrain the probabilities for an Earth visit by a settling civilization before a given time horizon. These results break the link between Hart's famous "Fact A" (no interstellar visitors on Earth now) and the conclusion that humans must, therefore, be the only technological civilization in the galaxy.

physics.pop-ph↗

arXiv2020

Effects of Radiation Pressure on the Evaporative Wind of HD 209458b

The role of radiation pressure in shaping exoplanet photoevaporation remains a topic of contention. Radiation pressure from the exoplanet's host star has been proposed as a mechanism to drive the escaping atmosphere into a "cometary" tail and explain the high velocities observed in systems where mass loss is occurring. In this paper we present results from high-resolution 3-D hydrodynamic simulations of a planet similar to HD 209458b. We self-consistently launch a wind flowing outward from the planet by calculating the ionization and heating resulting from incident high-energy radiation, and account for radiation pressure. We first present a simplified calculation, setting a limit on the Lyman-$α$ flux required to drive the photo-evaporated planetary material to larger radii and line-of-sight velocities. We then present the results of our simulations, which confirm the limits determined by our analytic calculation. We thus demonstrate that, within the limits of our hydrodynamic simulation and for the Lyman-$α$ fluxes expected for HD 209458, radiation pressure is unlikely to significantly affect photoevaporative winds or to explain the high velocities at which wind material is observed, though further possibilities remain to be investigated.

astro-ph.EP↗

arXiv2019

How Drag Force Evolves in Global Common Envelope Simulations

We compute the forces, torque and rate of work on the companion-core binary due to drag in global simulations of common envelope (CE) evolution for three different companion masses. Our simulations help to delineate regimes when conventional analytic drag force approximations are applicable. During and just prior to the first periastron passage of the in-spiral phase, the drag force is reasonably approximated by conventional analytic theory and peaks at values proportional to the companion mass. Good agreement between global and local 3D "wind tunnel" simulations, including similar net drag force and flow pattern, is obtained for comparable regions of parameter space. However, subsequent to the first periastron passage, the drag force is up to an order of magnitude smaller than theoretical predictions, quasi-steady, and depends only weakly on companion mass. The discrepancy is exacerbated for larger companion mass and when the inter-particle separation reduces to the Bondi-Hoyle-Lyttleton accretion radius, creating a turbulent thermalized region. Greater flow symmetry during this phase leads to near balance of opposing gravitational forces in front of and behind the companion, hence a small net drag. The reduced drag force at late times helps explain why companion-core separations necessary for envelope ejection are not reached by the end of limited duration CE simulations.

astro-ph.SR↗